Solid high-energy compositions, such as propellants, explosives, gasifiers, or the like, comprise solid particulates, such as fuel particulates and/or oxidizer particulates, dispersed and immobilized throughout a binder matrix comprising an elastomeric polymer.
Binders previously used in composite solid propellant formulations have generally been non-energetic polymers such as polycaprolactones, polyethyleneglycols or polybutadienes. Since about 1950 there has been a considerable need to develop energetic binders with satisfactory mechanical properties in order to provide safer binders at higher energy levels and to increase the energy level or specific impulse in a propellant formulation. For the most part only nitrocellulose has found usefulness as an energetic polymer binder. However, nitrocellulose suffers from undesirable mechanical properties. Alternatively, it has been proposed to employ conventional non-energetic polymer binders in combination with energetic plasticizers such as for example, nitroglycerine, butanetriol trinitrate, and trimethylolethane trinitrate. It has also been suggested that the energetic polymer nitrocellulose be employed with either non-energetic or energetic plasticizers in an attempt to improve mechanical properties. However, none of these proposals has led to fully acceptable energetic binder formulations.
Furthermore, there are many occasions when the use of plasticizers is undesirable or their use is not possible, such as when "clean" space motor/gas generator propellants or "clean" large launch vehicle propellants are required. The propellants used in the current generation of space motor/gas generator solid propellants, such as those used in small retro rockets to separate stages on launch vehicles, such as for satellite launch vehicles, e.g. Titan Retro, all employ about 84 wt. % ammonium perchlorate (AP) as the oxidizer and small amounts of aluminum, i.e. about 2% wt. Thus these propellants produce large amounts of gaseous HCl, about 18-20 mol %, and particulate Al.sub.2 O.sub.3 in their exhaust. The HCl and Al.sub.2 O.sub.3 can coat and/or destroy the optics and other sensitive parts of the satellites. There is therefore a need for solid propellants that could be used in these applications which would produce little or essentially no contamination or particles in their exhaust upon combustion.
There has been a continuing need for energetic polymers to be available for use in formulating solid high-energy compositions, such as propellants, explosives, gasifiers and the like. In this regard much recent work has centered on attempts to produce acceptable energetic polymers of glycidyl azide polymer and poly(oxytanes). A problem with elastomeric binders formed from poly(oxytanes) is their tendency to have mechanical characteristics less than that which would be desirable for a high-energy composition, particularly for a rocket motor propellant. It is especially difficult to provide poly(oxytane) binders having adequate stress capabilities. On the other hand giycidyl azide polymer is synthesized by first polymerizing epichlorohydrin to poly(epichlorohydrin) which is then converted to glycidyl azide polymer by reaction with sodium azide in dimethylsulfoxide. Beside the lack of a simple synthesis process, the production of glycidyl azide polymer requires relatively expensive reagents. Moreover, even after the polymer is synthesized it has been found that unplasticized glycidyl azide polymer-ammonium perchlorate solid propellants require about 78% solids to optimize Isp at about 254 sec.
Since the early 1950's poly(glycidyl nitrate), hereinafter referred to as PGN, has been known and recognized as a possible energetic prepolymer. The initial work on PGN was done by Thelan et al. at the Naval Ordnance Test Station (NOTS, now the Naval Weapons Center, NWC). They studied the polymerization of glycidyl nitrate by a variety of Lewis Acid catalysts with most of the work centering on the use of stannic chloride as a catalyst. No propellants were prepared by the NOTS workers and they noted that one drawback to their synthesis was the laborious purification procedure.
PGN AND PGN propellants were next examined at the Jet Propulsion Laboratory (JPL) by Ingnam and Nichols and at Aerojet General Corporation by Shookhoff and Klotz. The JPL workers found that PGN made using boron trifluoride etherate was low in both functionality (i.e. &lt;2) and molecular weight (MW=1500) and therefore polyurethane propellants made from this PGN had poor mechanical properties. Similar observations were made by the Aerojet workers. In summary, it has long been recognized that PGN may be an excellent energetic polymer but until now a method of synthesis could not be found that would produce nearly difunctional material with acceptable hydroxyl equivalent weights. Nor has it been possible to formulate acceptable unplasticized "clean" PGN space motor/gas generator solid propellants having reduced levels of solids.
It is therefore desirable to provide a family of high energy, clean, space motor/gas generator solid propellants and particularly such propellants which produce essentially no Al.sub.2 O.sub.3, HCl or chloride ion or particles in their exhaust. A further object of this invention is to provide such a family of high energy, clean, space motor/gas generator solid propellants which employ ammonium nitrate as the oxidizer and do not require the use of ammonium perchlorate as the oxidizer nor aluminum as the fuel. A still further object of this invention is to provide such clean, space motor/gas generator solid propellants containing PGN elastomer binder, ammonium nitrate oxidizer and boron. An even further object of this invention is to provide such high energy, clean, space motor/gas generator solid propellants requiring reduced solids loading to obtain optimized performance as measured by the specific impulse of the propellants and yet producing essentially no Al.sub.2 O.sub.3, HCl or chloride ions or particles in their exhaust. Yet another object of this invention is to provide such high energy, clean, solid propellants which perform as well as or better than the current space motor/gas generator solid propellants but which produce essentially no HCl or chloride ions in their exhaust.